This invention relates to an electrophotographic copying apparatus comprising scanning and exposing means for effecting optical scanning of a document to expose a photosensitive member in the form of an endless belt (photosensitive belt for short) to an optical image of the document while the photosensitive belt is moving, so as to form images of the document in a predetermined position on the photosensitive belt.
Electrophotographic copying apparatus of the moving photosensitive member and slit exposure type include two types: one is a document moving and scanning type and the other is an image forming system moving and scanning type. In the former type, when it is desired to raise the duplicating speed (the number of copies produced per unit hour), it is necessary to shorten the return time or raise the return speed while the copying processing speed remains unchanged. However, this gives rise to problems with regard to displacement of the document and safety of the operator. Particularly when copying of the original is performed in a scale reducing mode, the speed at which scanning is effected should be raised and this involves danger.
To solve the aforesaid problems of the prior art, proposals have been made to use an apparatus provided with a sheet mode separately to raise the duplicating speed without expediting the movement of the document. However, this apparatus has no effect in solving the problems by a book type document when copying thereof is carried out.
In apparatus of the stationary document and moving image forming system type, the return time is wasted as is the case with apparatus of the moving document type. Thus it has hitherto been the usual practice to raise the return speed to increase the duplicating speed. However, an apparatus based on an entirely different concept has been proposed in which the duplicating speed is increased by increasing the number of copies produced while holding a latent image obtained by a single scanning and exposing operation for use to perform a prolonged copying operation. In this case, the conditions under which processing is effected would undergo changes, so that difficulties would be encountered in producing copies of high quality. Moreover, when the copies produced are small in size, there would be the disadvantage that the non-image forming section takes too long in view of the condition of using the closed loop photosensitive member, such as a photosensitive belt, and the processing elements.
When copying is performed in an enlarging or reducing mode by means of an electrophotographic copying apparatus of the slit exposure type, varying the magnification can be attained in a direction perpendicular to the slit, for example, by changing the speed of travel of the photosensitive member. However, when the speed at which the photosensitive member travels is changed in performing copying by using apparatus of the prior art, a change in the speed of travel of the photosensitive member of the exposing section inevitably results in a change in the speeds at which portions performing other processing than exposing move, thereby causing a change to occur in the processing conditions and making it impossible to obtain copies of high quality. An added disadvantage is that the copies show a variation in output speed depending on the magnification.